I need external beam radiation for prostate cancer, will it have any bad effects on the rest of me?

Radiation proctitis: I can only tell you what i see as a gastroenterologist. Radiation can cause inflammatory changes in the lining of the rectum called radiation proctitis. It can be treated by a gastroenterologist with argon gas therapy if it occurs. Good luck.

not too bad: The majority of men do very well with radiation. During treatment there can be some fatigue, urinary changes and possibly some loose stools. Late term there can be a risk for erectile dysfunction, small risk for long term urinary changes, and especially with newer radiation techniques a small chance of rectal bleeding (proctitis).

Outcomes for: Prostate cancer compare quite favorably with surgery: they now have robots; we now have techniques that limit doses to healthy tissues. Proctitis rate is about 3%. Some depends on target, dose, genetic issues. Fatigue is in 1/3; no longer does any one get loose bowels. Erectile dysfunction depends on what you bring: we do not restore magic to wands that do not work. Age, smoking, dm, lipids add.